King George VI order the secret operation to hide the jewels in an operation was so closely guarded that the Queen only learned exactly what happened to the jewels during the filming of a BBC documentary, The Times reported.
A trapdoor used to access the secret area at Windsor Castle, where the Queen spent her war years for safety, still exists today.
He described how the most precious jewels were removed from the Imperial State Crown - worn at the state opening of parliament - so they could be kept separately in case of emergency.
In a conversation, with the royal commentator Alastair Bruce, Her Majesty reveals the crown was shortened by an inch for her coronation and was much larger when worn by her father George VI's coronation in 1937.
Mr Bruce, who presents the documentary, told the: 'What was so lovely was that the Queen had no knowledge of it.
In a rare interview, the Queen herself seems to marvel at seeing the imperial crown she wore at the time, recalling how heavy it was.
The Queen may enjoy the great privilege of wearing a crown, but the extravagant headpiece doesn't come without its downside.
Jenna Coleman plays young Queen Victoria in the series “Victoria.”
"The only word I can come up with is medicinal, like cough syrup", she said.
The Queen speaks candidly and with humour about the experience of her own coronation and the symbolic importance of artefacts associated with the sovereign in the one-hour programme. "You have to take the speech up because if you did, your neck would break and [the crown] would fall off".
"You can't look down to read the speech, you have to take the speech up". "But once you put it on, it stays".
"There are some disadvantages to crowns but otherwise they are quite important things". "I mean, it just remains on'".
Apparently the royal golden carriage was also pretty uncomortable - or to use the Queen's word, "horrible".
Queen Elizabeth on the day of her coronation (gracefully avoiding any appearance of neck strain).
The Coronation is part of the Royal Collection Season on BBC and will air this Sunday.